In recent electrophotographic printing in which an image is formed by line scanning with a laser beam, a semi-conductor laser having an oscillation wavelength in the longer wavelength region of 750 nm or more has frequently been used. Accordingly, electrophotographic photoreceptors exhibiting satisfactory electrophotographic characteristics to long wavelength light have been demanded. In order to obtain satisfactory image qualities with the electrophotographic photoreceptors sensitive to long wavelength light, one must settle down the problems: the interference fringe appearing on image formation and image defects such as white spots (or black spots in the case of reversal development system).
The former problem is deemed ascribed to the phenomenon that transmitted light which has not absorbed in a photosensitive layer is regularly reflected in the inside of the photosensitive layer and the substrate to generate multiple reflection of a laser beam thereby causing inference with the reflected light on the surface of the photosensitive layer. The latter problem is deemed ascribed to coating defects of a photosensitive layer and impurities incorporated into a photosensitive layer, such as different ions, different elements, different particles, and dust. It has therefore been demanded to develop a photosensitive layer free from coating defects and impurities.
It has been proposed to roughen the surface of a substrate for an electrophotographic photoreceptor by wet honing with a suspension of an abrasive to thereby overcome the above-mentioned two problems at a time as disclosed, e.g., in JP-A-2-87154 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Wet honing holds advantages such that surface roughening can easily be achieved in a short processing time in a stable manner; desired surface roughness can be obtained with precision; and the roughness obtained is uniform with little abnormal unevenness which causes coating defects. On account of these advantages, wet honing is superior to other surface treatments such as anodizing and buffing from the considerations both of production and image quality stability against white spots or interference fringe.
Conventional wet honing techniques are effective to meet the problems of interference fringe and white spots due to coating defects arising from abnormal unevenness of the substrate but still ineffective to eliminate image defects arising from impurities attaching to the substrate. That is, because abrasives currently employed in wet honing contains impurities such as different ions, different particles and dust, spraying of such abrasives to a conductive support is accompanied by adhesion of the impurities onto the conductive substrate. The impurities adhered to the conductive substrate induce denaturation of the conductive substrate or photosensitive layer thereon, interference with formation of a uniform subbing layer on the substrate, and reduction in adhesion between the conductive substrate and the subbing layer. As a result, parts where carriers are injected into the photosensitive layer are formed, leading to image defects.
Removal of the impurities by washing a conductive substrate has been studied. However, the impurities once having entered into the valleys of the roughened surface of a substrate have stronger adhesion than those attaching to the substrate before being roughened and are therefore very difficult to remove by washing.